Ultra high frequency oscillator



Feb. 24,1948.

J. A. MORTON 11mm men FREQUENCY OSCILLATOR Filed Au 28, i945 //v v/vronJ. A. MORTON by; T

ATTORNEY Patented Feb. 24, 1 948 ULTRA HIGH FREQUENCY OSCILLATOR Jack A.Morton, Plainfield, N. J., assignor to Bell Telephone Laboratories,Incorporated, New York, N. Y., a corporation of New York ApplicationAugust 28, 1943, Serial No. 500,321

6 Claims. 1

This invention relates to ultra-high frequency oscillators andparticularly to means adapting its lower frequency prototype circuit,which embodies the conventional use of a space charge triode and aregenerative coupling between its output and input circuits, toefficient operation at the extremely high frequencies here concerned,which are in the centimeter range. I The generic object of theinvention, conformable to the above, is to provide a simple butefficient feedback amplifier within the ultra-high frequency range. Morespecific objects will be given, as having greater pertinency and meaningat that place, following a brief descziption Of the invention in theaspects which are deemed patentably novel.

In the operation of oscillators in the ultra-high frequency range it hasbeen found that circuits having distributed constants are superior tolumped constant circuits for frequency determination, feedback coupling,and the like. The present invention employs a cavity resonator, as theterm is generically used, and the requirements may be satisfied byvarious forms of the same of which a section of coaxial conductor ispresently favored. Sucha form of cavit resonator, sometimes denominatedcoaxial cavity and sometimes merely by the term .coaxial, comprises in asimple form, as adapted for present purposes, a hollow cylindricaloutside conductor or shield element having closed ends and a cooperatinginner conductor which is coaxial with the same and connected, through acapacitance, at one end with the closure element of the outsideconductor, leaving ,the other end insulated.

The teachings of the present invention make possible the use of a singlecavity resonator with the electrode enclosing part of the space chargetriode tube within its envelope. The tube has its electrodes related tothe resonatorin the specific manner that confers novelty and utility, ina patentable sense, on the invention. The idea of a single cavity issignificant since priorpractice, and the more obvious practice wouldprovide two cavitymembers, one between the cathode and control electrodeand the other between the control electrode and anode. The aboveresonatorelectrode relations are satisfied for th present single cavityoscillator by positioning the tube adjacent one end of the resonator,namely, that end adjacent the'insulated end of the inner conductor, andby an alternating current connection from the cathode to the near endofthe outer conductor, a similar connection from the anode to' 'the freeend of the inner conductor and a likeedance Z to be described from thecontrol electrode to the inner cylindrical wall element of the outerconductor at a point spaced from the closure elements thereof atrelative distances depending on conditions for most effective operation.

One result of the connections as above, as is indicated by thesimplified schematic to be described in detail later, is that thecircuit is a variant of the conventional Hartley feedback oscillator,differing to the extent that the connections of the cathode and controlelectrodes have been inverted as compared thereto so that the cathode isconnected to the end of the inductance instead of to an intermediatepoint thereon. The reason for this expedient, and the structure of theinvention which makes possible its effective realization, is that at theextremely high frequencies concerned the electron transit time fromcathode to anode becomes of significance in relation to the cycle timeof the resultant characteristic oscillations, instead of having aninsignificant relative value as in the prior art relating to otherwisesimilar devices operating at lower frequencies.

The Hartley circuit in mind is Well disclosed in United States Patent1,356,763, October 26, 1920. The positioning of a cathode tapintermediate the anode and control electrode taps of the Hartley circuitresults in a phase reversal attending the regenerative feedback from theoutput to the input circuit of the tube, which compensates for theinherent -degree phase shift in the tube itself, and therefore makespossible the 360-degree (or, which amounts to the same thing, aneffective O-degree) phase shift in the round trip path as a whole whichis necessary in order to perpetuate the effects of a given impulse atthe anode by the cyclical recurrence of successive impulses in likephase at that point. However, at the high frequencies here concerned therelatively long electron transit time itself tends to compensate for theinherent phase shift of the tube so as to make possible an optimumfeedback without complete phase reversal in the external circuit. It isnecessary to add some phase shift, depending on the frequency range, forexample, as would be provided by impedance Z to be described. Anotherillustration of this particular expedient, although not practiced in thesame electrical and structural environment as in the present instance,may be seen in Fig. 3 of United States patent to Heising 2,068,324, January 19, 1937. An example of a type of tube,

which is well adapted for the present purpose is the General Electrictube known as the GL-446. Although this tube is characterized by smallspacings between electrodes and therefore by as small transit times asmay be achieved by tube design, the invention is not limited to the useof tubes which are extreme as to interelectrode spacing.

Although it is characteristic of the circuit of the invention that itlends itself well to'the above expedients, that is, the achievement ofan optimum phase condition and the use of a singlecavity resonator, theinvention, especially as to the relation of the tube elements to thesurrounding coaxial cavity, has other characteristicswhich distinguishit from the priorart andwhich PTO.- mote the above generic object of theinvention. The positioning of the electrode enclosing part of the tubewithin the structure which simulates the usual frequency determiningcircuit not only promotes conservation of space and physical andelectrical protectio'nfor the tube but even makes possible an efficient.organization as a whole by preventing undesirable radiation and couplingeffects on account of the tubeelements themselves and their connections.The particular ordering of the connections of the tube electrodes to thecoaxial cavity makes this possible besides makingpossible theaboveavoidance of phase. reversal. It shouldlbe-noted that the avoidance ofsuch phase reversal as achieved by said ordering, even at these veryhigh frequenciesv and with the indicated tube, is not necessary sincethe requisite 360-degree over-all phase shift could be achieved in otherways.

The prime advantageszofthe'single cavity oscillator asdistinguished-from a double cavity oscillator, appear to: derive fromthe mechanical simplicity obtainable. The fact. that but one frequencydetermining circuit is usedmakes possible frequency adjustmentsibvasingle simple control. Moreover, the absence of any other frequencydetermining elements precludes the possibility of a. hopping backandforth from one frequency to the other as has been postulated as a causeof blockingfor somev double cavity oscillators.

Consistently with the above statement of the characteristics oftheinvention, a'more specific object of the invention is to achieve anultrahigh frequency oscillatorusing. a single. cavity resonator with thebenefits. tending to be conferred thereby as just. en-um'eratedxand morepar ticularly where the whole tube structure is enclosed in said. singleresonator with the additional benefits thereby conferred having to dowith conservation of space and resultant physi cal and electricalprotection for said tube, as well as avoidance of undesirable radiationand cowpling effects, also as above enumerated.

This invention canbe more readily understood by reference to thefollowing detailed description of one embodiment as shown in the drawingin which:

cathode 3 shown partially diagrammatically with its heater 4 whosesource is not shown, control electrode 5, and anode 6. Batteries, orother equivalent direct potential sources, are shown associated withthese electrodes in conventional manner. The frequency determiningcoaxial con the tube, overlap and are related in such a way that theflend-phase reversal in the feedback from the anode to the controlelectrode. This results from the" connection of the cathode instead ofthe; control-, element, to the end of the effective coil element, shownin schematic Fig. 2 as a conductor of a transmission line simulating theinductance element of the coaxial of Fig. 1. The significance ofthistcircuit arrangement is as pointed out in the statement-ofinvention; That is, the c'o'ntroli electrodelead terminates in a tap 8(best shown in Fig. 2) movable on the effective inductance-element ofthezfrequencydetermining' circuit, 2. The positioniof the tap determinesthe degree of feedback. In practicethis. tap is adjusted for maximumpowerfoutput. This. lead includes an impedance Z shownin block; Thisimpedance provides means'for phase adjustment, as pointed out in thestatement of in-- vention. Its character; depends upon the fre-.-quency' and hence; upon. the phase. shift needed. It may be, forexample",v an RC circuit; or a co;- axial adjustable stub. In someinstances a simple wire connection is adequate. In Fig. I a, co.- axialadjustable stubis Shown. The resistance element 9 is a high frequencyresistance through which the anode current is supplied-withoutshort-circuitingtheifrequency determining circuit. For thisreasonitsh'ould be of-a high value.

and low loss so as not to absorb energy from said circuit. Condenser flisfoi the purpose of pre venting any high frequency-currents which areinduced in resistance 9 from fiowingoutsi'de to some non-useful load:Toth-i's end-resistance 9 the line so long a -i-t's highfrequencyimpedance is large as compared to"- the' impedance of the lineat that point.- Electricallyit should beplaced at the lowest impedancepoint for it to have least efiect on the high frequency behavior.

In Fig.- 1 the structural elements of-the oscillator are shown with :thesame label ing as in Fig.

2. It is evident from the-showing of the tube I' that it is adaptedfor-its-purpose here disclosed, or the like, although it should beunderstood that the invention in its patentably novel aspects has norelationto the particular structure of the tube and widely varyingforms" of the tube could be used. The particular tube here shown mightwell be the General Electric tube known by the designation Gib-446whichis well adapted for connection to a cavity'resonator because of therelative directions of extension of the-electrodes, their respectiveconfigurations, and the like. The equivalent frequency determiningcircuit is con-. stituted by the coaxial comprising. shield or outerconductor element ill closed at the-end remote from the tube by closureelement l I: and, atithe tube end, by the metallic member l2: of thetube to which it may beattached byfrictional means I a e -see or thelike. The inner conductor of the coaxial is indicated byreferencenumeral l3. It is divided near its end remote from the tube toconstitute. av variable. condenser M: which simulates the tuningcondenser. similarly identified in Fig. 2, although in the. absence of acondenser. the circuit would operate by reason of the equivalentinterelectrode.capacitancesof the tube except that unless this.expedient were used it might be .difiicult to achieve the desiredfrequency. Alternatively, the condenser could be dispensed with in:favor. of a variable. length cavity. T111831.

ternative is deemed too obvious and sim le to require illustration. Thiscondenser is made operative by the manually operated slidable, .ortrombone, operating member IS. The cathode is made an integral part ofthe associated structure by the particular mounting shown in which it isinsulatingly separated by means Hi from the metallic element l2 of thetube which is electrically integral with the coaxial. This provides analternating current connection between the cathode and'grid or frequencydetermining circuit while maintaining a direct current separationtherebetween. The resultant equivalent capacitor is indicated by thelabel la, this being indicated in Fig. 2 as well. The anode supply isshown in Fig. 1 as coming from a circuit terminating at I! where it isconnected to the high frequency resistance element 9. An alternatingcurrent connection between the junction of the anode source andresistance 9 on the one hand and the coaxial cavity on the other hand isachieved by the condenser action between the inner surface of the outerconductor l and the condenser electrode-simulating element It, theequivalent condenser being identified as For the sake of simplicity nomeans are shown in Fig. 1 for applying a biasing potential to thecontrol electrode as shown in Fig. 2. Said control electrode is showndirectly connected to the coaxial through impedance Z, as in Fig. 2,although in Fig. 1 this impedance is shown in one of its specific forms,namely, as a coaxial adjustable stub. An energy take-oil for a load isshown schematically by output coil l 9 magnetically coupled to thecoaxial and connected to load simulating resistance 20.

It appears from the above-detailed description that an oscillator havingthe circuit characteristics as illustrated by Fig. 2 has beenconstituted by the structure disclosed in Fig. 1 comprising a spacecharge triode which is completely enclosed in the coaxial cavity andhaving its respective electrodes connected in a particular manner to theelements of said coaxial cavity.

Although a certain specific embodiment of the invention has been shownand described, it will be understood, of course, that variousmodifications may be made therein without departing from the scope andspirit of this invention as defined in the appended claims.

What is claimed is:

1. A regenerative electron tube oscillator comprising, an electron tubehaving an electrode enclosing part including a cathode and two coldelectrodes, and a single cavity resonator which, in combination with theinterelectrode capacitances of the tube, constitutes a parallelresonance inductor-capacitor circuit for determining the frequency ofsaid-oscillator, at least the electrode enclosing part of said tubebeing within said resonator and constituting a closure means at one endthereof, the cathode being connected to said end, a substantial portionof the inductorcapacitor circuit being directly coupled between?said'ca'thode'. and one of said 'cold electrodes and the other coldelectrode being connected to the inductorportion of said resonatorintermediate the above. said connection points of the cathode andfirst-mentioned cold electrode.

2. "An ultra-high frequency oscillator comprising, a space charge triodetube having an electrode enclosing. part including a cathode and twogcold electrodes, and .a single coaxial cavity reso- ,and one coldelectrode thereof being directly coupled to the cavity resonator atpoints between which substantial alternate potentials occur during theoperation of the oscillator, and the other cold electrode beingconnected to a point of the resonator intermediate thereof.

3. The oscillator recited in claim 1 in which said triode tubecomprises, a cathode, a control electrode and an anode, of which thecathode and anode provide the recited connections to theinductor-capacitor circuit, the control electrode being connected to apoint of the resonator intermediate the cathode and anode connectionpoints.

4. An ultra-high frequency oscillator comprising, a space charge triodeincluding a cathode, and a grid and anode aligned therewith, a singlecoaxial cavity resonator including an outer hollow cylindrical conductorsubstantially closed at either end and a coaxial inner conductorcomprising spacially separated portions effectively providing a gapintermediate its ends, said inner conductor being connected at one endto one end of the outer conductor and having its other end electricallyinsulated from said outer conductor, said triode tube constituting aclosure means for the other end of said outer conductor, at least theelectrode enclosing part of said tube being within said outer conductorof the coaxial cavity resonator, a direct coupling from the anode to theinsulated end of the inner conductor, a direct coupling from the cathodeto the end of the outer conductor which is opposed to said insulated endof the inner conductor, and a connection from the control electrode to apoint on the inner surface of the outer conductor intermediate the endsthereof.

5. The oscillator recited in claim 4 including means mounting saidspacially separated por-' tions of the inner conductor and adapted toper mit relative motion therebetween and including an actuating meansfor at least one of said portions whereby to vary the length of said gapand therefore the capacitance between said portions.

6. An ultra-high frequency oscillator comprising, a space charge triodetube having a cathode, a control electrode and an anode, a singlecoaxial cavity resonator comprising an outer hollow cylindricalconductor enclosed at each end and a concentric inner conductorcomprising spacially separated portions effectively providing, a gapintermediate its ends, said inner conductor being connected at the oneend to a given end of the outer conductor and with its other end, whichis electrically insulated from said outer conductor, extending adistance substantially short of the opposite end of the outer conductor,said triode tube being mounted inside th outer conductor, constituting aclosure means at said opposite end of the outer conductor and within thespace between the insulated end of aasmsea REFERENCES CITED Thefollowing references are of record in the file of this patent:

UNITED STATES PATENTS Name, Date Gurewitsch. ..-'...'I -I0v. 19, 1946Turner -Sept. 24, 1946 Whinnery July 16, 1946 Chevignyv NOV. 2, 1943'Kohler Feb; 10, 1942 Allerdinget a1. Dem-31, 1940 Unk July 29, 1941McA'rthur May 26, 1942 McArthur July 18, 1944'

